Color tube mask positioner



Feb. 25, 1958 J. CHRISTOFFERSON 2,824,989"

COLOR TUBE MASK POSITIONER Filed Dec. 21, 1954 R m m w.

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COLOR TUBE MASK-POSITIONER James Christoiferson, West Newbury, Mass, assignorto Columbia Broadcasting System, Ina, Danvers, Mass,

a corporation of New York, dtiing business under the name of CBS-Hytron, a division Application December 21, 11954, Serial No. 476,635 scia ims. ((11.313-85) All three electron streams emanating from the guns may 1 be deflected and focused by common systemsto Converge at closely spaced points on the face of the tube. The screen on which the electron streams impinge is' composed of symmetrically arranged arrays of three dots of luminescent materials or phosphors deposited directly on the face of the tube. One phosphor" emits a red lig'lit'when struck by an electron stream; the second, green; and the third, blue. A filtering device, called a shadow mask, is placed between the guns and the screen. This mask is a thin conducting sheet in which holes are symmetrically disposed to allow only the electron stream. from the corresponding gun to fall on phosphors of a given colorproducing type. 7

Limitations in present manufacturing techniques make it mandatory that each array of dots of a given phosphor be formed consecutively using the same shadow mask as a photographic negative. One of the color phosphors is first settled on the screen and the dots are formed by exposure of the phosphor through the, shadow mask by a light placed at the same'position 'as will be occupied by the corresponding gun in the tube. The dots are then fixed by wet photographic techniques. The same process is repeated to obtain the last two arrays of dots. The shadow mask must be removed to allow development of each'array of dots and accurately positioned each time a color phosphor is formed'on the screen. Ease of handling to reduce manufacturing costs dictates a removable yet positive positioning means for these step Standard practice has been to use a spring type hold-down device which can be removed and reinserted when necessary in processing the screen.

After some intermediate steps, not material here, the shadow mask is again assembled to the screen and the assembly is subjected to elevated temperatures to remove all volatile impurities. The shadow mask must maintain its correct position during and after this treatment. The positioning means must not be affected by relatively high temperatures. Ordinary spring materials sometimes lose a substantial amount of their resiliency during this operation. Therefore, a simple spring type hold-down device, although adequate to hold the mask in position and ma sonably suitable for screen processing, may be improved upon considerably.

Of course, any positioning means used must prevent any substantial movement of the shadow mask when it is subjected to accelerating forces or mechanical shock during shipment and use. Asubstantial permanent dislodg- 2,824,989 Patented Feb. 25,- 1958 meat of the mask willc'ause mis-regis'tration of theelec tron beams, causing'false colors toappearto the-viewen of the screen. Again, a simple spring type hold-downdevice sometimes fails to positively hold the mask in position. t V 7 A further important consideration making it desirable to maintain a firm mechanical contact between the shadow maskand the screen base is the'necessity'offbonding the two parts electrically. If the shadow mask is at a dif-v fent potential than the scre'en,'the electronstreams are affected adversely. A spring type liold down device does not ensure a firm electrical contact between the mask. and

screen.

Unfortunately, the degree of resiliency:of'ttiepositioning means desired for I V is detrimental after assembly. At'the'sanie iiIIle, absolutely rigid 'positioningmeans can not answer the. prob.

lem'after assembly since some resiliency must be present to compensate for differentialexpansion and shock,

The necessity of maintaininga small amount of;resil-- iency in the positioning means may beseenm'ore clearly' if the operating temperature of the shadow ma skand tube assembly is considered. Power'in'the order of twenty to fifty watts'is dissipated in presently manufactured tubes; with shadow masks. The temperature'rise of the parts; being considered. is approximately 1- C per watt dis sipated. It is evident that, if the dissii'riila'r'materials of? which the parts are made areri'g'idly bondedftogether large internal strains will result. Thefs't'rains, unless;re--

lieved, will quicklyexceed the elastic'liiznits 'off the various tion for the mask are best obtained'from the glass wall of the tube, it would be most logical to hold the maskin place with a support made from glass. This glass would be the samematerial'as theglass 6f thetubewa ll to which the copper is, being positioned. There are, however, many metallic materials. which have 'coeflic'i'ent's of expansion matching those of particular type'sof glass. An example of a material having a suitable coefficient is that'with the trade name Kovar. Since frnetallic materials are-gener-ally more easily fabricated than glas'sga metallic device having such properties'is preferred in the present invention.

No positioning device exists in the fiel d of electron tubes: which completely answers the problems. Any device. which will adequately solve the foregoing problems would constitute a eonsicle'rabl'e advance in thec'o lo r television- 8.1T.

Therefore, it is an'objec'tof this invention: to provide positive positioning means in a color picture tube which are easily removable during preliminary manufacturing stages.

It is a further object of this invention to provide means incorporating an adjustable'a'mount of resiliency to allow difierential expansion without loss of registration of the Another object of this invention is to minimize they? amount of resiliency required in a positioning means for preliminary manufa'cturingtstagn rsista'nce :electrical contact between the shadow; mask :and screen fa color picture'tube 'regardless of the 7 "conditions of use of'the assembly. 7 a

V ":In general, the objects of this inventlon areattained "by means off'a number of identical elongated adjustable I the end of the spacing bar 19 after assembly of the hold-i down device for the final time in the tube. W

The foregoing explanation is a detailed description of a proven embodiment of the invention. In 'the actual tube, several similar positioning devices are insertedaround the periphery of the shadow mask 21 to match the remaining number of sp'hericalbossesZO. The length V of each positioning'device is automatically adju sted to 7 equal the distance between-eachspheiicalboss zll and I, the. nearest point onfiange -ZZ. I The end of the elongated .fspacersgpositioned around the peripherypf the shadow l jmask 'lfiach spacer is composed basically of a fixed memf her, a 'sliding'member, telescopically mounted on the spacing bar 19 is affixed to the shadow mask 21. The shadow mask 21 is set in place on. the s'phericalbosses ably. mounted element ffiiedinember, a spring between the sliding'and fixed "members and an adjustable stop attached to the sliding .20. The slidably mounted tubular element 11 is pressed toward the shadow mask 21 against the pressureofthe member. s 7 7 helical spring 18 until the cut;12 fits against the flange 22-. The viewing end of the bulb is shaped somewhat like The slidably mounted tubular element ll'is then released a bowlwitha. flat bottom, T h screen i deposited on and the spring 18 holds the positioning device in position.

7 the inside surface-of the viewing 'end. Spherical bosses 'Until the stop 14 isadjusted to bear against the end V are-molded in the bulb adjacent the edge of the screen. Ofthe spacing bar. 19, only the force'of the spring 18 holds annular flange is fixed adjacent the viewing end pro- 20 the Positioning device in Position and the eay jecting int o the bulb. The shadow mask is'indexed tothe disengaged simply by reversing the assembly procedure. sphericalibosses'. The adjustable, spacers are inserted Afterthe stop14has been adjusted, the maximum over theishadow mask at each spherical boss. The free length of F Positioning device fiXedh l' end of thespacer'is pressed to shorten the spacer and t. is made so that h x um l g is t y' allow the free end of the spacer to be slipped under the less than the distance between each. spherical boss 20 flanges The spring tension holds the endsof each spacer and the CIQSeSi Ph 0f the flange 2- her or the in position regardless of the variations in distance between a helical P 18 remains active, hili limited in e am each spherical boss and the edge'of the fflange. After it may change. the overall length of the positioning the operations'between which removal oflthe mask isv Viee, thus making ss mbly i a ly re ilien V necessary, the adjustable stop is moved to limit the amount During the' preliminary manufacturing stages, a the 'th fix d and Sliding element may telescope. The adshadow mask 21'ispositioned and removed three' times.

. justment of the stop may be. done..very accurately with e h im n rms/p o of. l n s ntma ei i l the sp acerin' its' final position t o obtain any desired is fd the glass pa 3- re ab y t -P st amount of resiliency to the whole assembly. a

' tioners as hereinbeforeidescribedare hinged atfthe flange 1 For further objects of'this invention; reference should h'i -V- Each h a r yo doisis be flmade" to the following dr'awing', the single figure of toihe formed, h Shadow 35 S'-'P d Oh. the":

V which represents a practicalembodiment of the principles hemispherical bosses z -f hQ iQW tubular elem .ofgthe invention; There is actually illustrated in-the' 11 is pressedto shorten the overall length of each posidrawing a partial cross-section of a tube'as's emblysho w h The Posiiiehers a then i d until he c s 1 ing the manner in which the various parts are arranged y he mated with the edge of the hanger h: l3

. to obtain substantially rigid spacing but an adjustable tubular l n a n released. The ic amount -of r e sfliermy' For Convenience and ease .of springs18 force the tubular, elements into fflunderstanding; only one positioner is shown. In pracriiollal g g t h e flange .h c s 1 I e.

tice, several similar positioners are disposed around the stops 14 are retracted With 13 fie w i o her S tperiphery. able tool so that they do not coact with the spacings bars Referring to the drawing,:an elongated spacing bar 19 19 dlliiflg these P Remove! f. the Shadow k a is shown with a hollow tubular element 11 slidablymountis accomplished hypressihg and i the hhiiowi ed thereon. A flange 16"on one end of the spacing bar tubular elements illrltil h eis disengaged V 19 may be formed'as an "integral part th f Th from the cuts 12. The shadow mask 21 is then ,free to spacing bar is preferably made' from a material which 'belified oi h phe s t a has a coeificient of expansion substantially the same .as After the luminescent Screen a been co p 511 V the glass of the bulb, such asthat with 'the trade'name the glass panel 23 the a w; m s 2 i a n; p i- Kovar. The ends of the Qflang'e 16 fit into upwardly tionsd as described'and the di b es p .1 i c w ex nding wings of a V-blo'ckf 17. The V-block 17 into the hollow tubular element ll' until it bears agziinst,

" matchesjone of the several spherical bosses 20 on 'the peiheefld of h Spacing e 9- e p 14 issiheh hacked riphery of the glass panel 23 of the tube as shown through ofir'a'mm'hr We to anowihe p ng to e r Slighh 1 holes in the periphery of theshadow mask "21; A helical m u esiiiehilY e w tubular n hd. i spring is mountedcoaxially around the spacing bar- 19 Spacing 1 V f r r 3 One end of the spring'lS; bears against the inner side-' Whei1 h mp ra of h ma '21 and'gp l Z t of theflange 16, Theotherrend of thesprin 1g. b s changes during operation, thedistance between the ;hemi-' 7 I againstthe .slidably mounted tubular element'ill. So ph ri alb s's 2.08mi h e a e tprima y I long it e p is in v coinp ressionjt exerts. a' force" because 9 i t s q F a ehe P i n? a I tending to move'the slidably mounted element 11 away mf t' ltself t e h n c dlsiance gh f h fl 1 and ,conseguently-away jfmm. {he '65 resiliency of the spring 18; Theamount of changegreindentation 17. yAtdiagonal cut'which may be of the qumid of 1 Spring 18 i q i i 1 1 t t spacing bar 19 from a materialhavmg substant ally the shape shown at 12 is made in the top surface of the 7 same coelficient of hnearexpansion as the glass panel 23..

V shdably mounted element 11.. A flange 22 lsllgldly at- 1 t I i a 7 Even if the spring 18 loses a substantlalamount ot llS tached to the viewing end 23. The edge ofthe flange 1 f h 1135' 22 to b come distance bwween theitwo ind 7th b a disengaged i lromthe cut 12 because the m nunun length r force s 1 Ices a Y the .of thepositioner' is fixed by'the stop P W111 w e' le length O The low resistance contact between the shadowmasl; t hoid'down e e i yj' VaflailOnS- ad- 21 and the panel 23 is a secoudaryjr e's ult of using aspac tablestop ;14 which may he. threaded into the slidingbar 19 fabricated from a 'material 'hayir'ig-substam tiallygthesame -coeflicient got,-llinear eigpansion as .the a panel 23. Since the flange 22 is intimately joined to the panel 23 and the flange 22 cannot disengage from the cut 12, a complete electrical path is maintained from the mask 21 through the positioner and flange 22.

While the foregoing description outlines a preferred embodiment of the invention, modifications will suggest themselves to those skilled in the art. The invention should not be restricted to the embodiment shown, but only by the spirit and scope of the claims appended hereto.

What is claimed is:

1. A color television picture tube having a shadow mask secured therein with a plurality of adjustably resilient retaining members within said tube each said retaining member being independently adjustable.

2. A color television picture tube having a shadow mask therein, means for resiliently mounting said shadow mask within said tube, and means for adjusting the degree of resiliency of said mounting means.

3. A color television picture tube having a shadow mask therein, means for resiliently mounting said shadow mask within said tube, and means for adjusting the degree of resiliency of said mounting means, the material from which said mounting means are fabricated having substantially the same coefficient of linear expansion as the material from which the said tube is made.

4. In a cathode ray tube having a shadow mask, apparatus for positioning said shadow mask at predetermined points therein comprising, a plurality of similar retaining members, each of said retaining members having first and second telescoping portions, each of said first portions being mounted on said shadow mask at one of said predetermined points, means springily attaching one each of said second portions to one each of said first portions, an adjustable stop mounted on each of said second pertions, each said adjustable stop coacting with one each of said first portions to vary the maximum telescoping of the first and second portions with which it is associated, and means in said tube for holding each of said second portions.

5. In a color television picture tube, apparatus for circumferentially supporting a shadow mask substantially against the periphery of the viewing screen comprising, a plurality of hold-down devices, each including first and second telescopically engaging members, the first member coacting with the said shadow mask, said second member coacting with a predetermined point on the inner wall of said tube, means springily joining said first and second members, and an adjustable stop whereby the telescoping of the said first and second members may be adjusted.

6. A hold-down device for the shadow mask in a color picture tube comprising, a retaining member having one portion thereof resiliently movable relative to a second portion thereof whereby the length of said retaining member is adjustable, said retaining member being formed of material having a coefficient of expansion matching that of the material of said tube, and disposed to resiliently retain said mask in a predetermined position relative to said tube.

7. In a til-color cathode ray tube in which a shadow mask is mounted between a source of electrons and a luminescent screen, an adjustable resilient positioner comprising, an elongated spacing bar attached to said shadow mask, a hollow element slidably mounted on said spacing bar, a helical spring coaxially mounted on said elongated spacing bar whereby said hollow element is urged away from said spacing bar, means indexing said hollow adjustable element to a predetermined point on the wall of said cathode ray tube, and an adjustable stop mounted on said hollow member coacting with said elongated spacing bar whereby the overall length of said spacing bar and hollow adjustable member may be substantially fixed.

8. In a glass color television picture tube, apparatus for circumferentially supporting a shadow mask comprising, a plurality of similar retaining members and a plurality of hemispherical bosses molded into said tube adjacent the viewing screen thereof, each of said similar retaining members including, a V-block having outwardly flaring portions, means attaching said outwardly flaring portions of said V-block substantially on the periphery of said shadow mask, an opening being formed in the periphery of said shadow mask adjacent the point of attachment of said V-block to accommodate a hemispherical boss, said V-block bearing on said spherical boss, an elongated spacing bar, the material from which said spacing baris fabricated having substantially the same coefiicient of linear expansion as the material from which the said tube is fabricated, means for hinging the first end of said spacing bar to said V-block, a hollow tubular member telescopically mounted over the second end of said spacing bar, a helical spring coaxially mounted on said spacing bar, one end of said spring being attached to said spacing bar, the other end of said spring being attached to said tubular member, means for securing said tubular member to a predetermined point on the inner wall of said tube, a screw thread impressed on the inner surface of said tubular element, and a set screw mating with said screw thread and coacting with said spacing bar to limit the amount of telescoping of said spacing bar and said tubular element.

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